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      <h2><a href="./">Go by Example 中文版</a>: 随机数</h2>
      
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            <p>Go 的 <code>math/rand</code> 包提供了<a href="http://en.wikipedia.org/wiki/Pseudorandom_number_generator">伪随机数</a>生成器。</p>

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            <a href="http://play.golang.org/p/Ueh4KLgIWw6"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
          <div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>

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          <div class="highlight"><pre><span class="kn">import</span> <span class="p">(</span>
    <span class="s">&quot;fmt&quot;</span>
    <span class="s">&quot;math/rand&quot;</span>
    <span class="s">&quot;time&quot;</span>
<span class="p">)</span>
</pre></div>

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          <div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
</pre></div>

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            <p>例如，<code>rand.Intn</code> 返回一个随机的整数 n，且 <code>0 &lt;= n &lt; 100</code>。</p>

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          <div class="highlight"><pre>    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Print</span><span class="p">(</span><span class="nx">rand</span><span class="p">.</span><span class="nx">Intn</span><span class="p">(</span><span class="mi">100</span><span class="p">),</span> <span class="s">&quot;,&quot;</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Print</span><span class="p">(</span><span class="nx">rand</span><span class="p">.</span><span class="nx">Intn</span><span class="p">(</span><span class="mi">100</span><span class="p">))</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">()</span>
</pre></div>

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            <p><code>rand.Float64</code> 返回一个64位浮点数 <code>f</code>，且 <code>0.0 &lt;= f &lt; 1.0</code>。</p>

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          <div class="highlight"><pre>    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">rand</span><span class="p">.</span><span class="nx">Float64</span><span class="p">())</span>
</pre></div>

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            <p>这个技巧可以用来生成其他范围的随机浮点数，
例如，<code>5.0 &lt;= f &lt; 10.0</code></p>

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          <div class="highlight"><pre>    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Print</span><span class="p">((</span><span class="nx">rand</span><span class="p">.</span><span class="nx">Float64</span><span class="p">()</span><span class="o">*</span><span class="mi">5</span><span class="p">)</span><span class="o">+</span><span class="mi">5</span><span class="p">,</span> <span class="s">&quot;,&quot;</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Print</span><span class="p">((</span><span class="nx">rand</span><span class="p">.</span><span class="nx">Float64</span><span class="p">()</span> <span class="o">*</span> <span class="mi">5</span><span class="p">)</span> <span class="o">+</span> <span class="mi">5</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">()</span>
</pre></div>

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            <p>默认情况下，给定的种子是确定的，每次都会产生相同的随机数数字序列。
要产生不同的数字序列，需要给定一个不同的种子。
注意，对于想要加密的随机数，使用此方法并不安全，
应该使用 <code>crypto/rand</code>。</p>

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          <div class="highlight"><pre>    <span class="nx">s1</span> <span class="o">:=</span> <span class="nx">rand</span><span class="p">.</span><span class="nx">NewSource</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">Now</span><span class="p">().</span><span class="nx">UnixNano</span><span class="p">())</span>
    <span class="nx">r1</span> <span class="o">:=</span> <span class="nx">rand</span><span class="p">.</span><span class="nx">New</span><span class="p">(</span><span class="nx">s1</span><span class="p">)</span>
</pre></div>

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            <p>调用上面返回的 <code>rand.Rand</code>，就像调用 <code>rand</code> 包中函数一样。</p>

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          <div class="highlight"><pre>    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Print</span><span class="p">(</span><span class="nx">r1</span><span class="p">.</span><span class="nx">Intn</span><span class="p">(</span><span class="mi">100</span><span class="p">),</span> <span class="s">&quot;,&quot;</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Print</span><span class="p">(</span><span class="nx">r1</span><span class="p">.</span><span class="nx">Intn</span><span class="p">(</span><span class="mi">100</span><span class="p">))</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">()</span>
</pre></div>

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            <p>如果使用相同种子生成的随机数生成器，会生成相同的随机数序列。</p>

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          <div class="highlight"><pre>    <span class="nx">s2</span> <span class="o">:=</span> <span class="nx">rand</span><span class="p">.</span><span class="nx">NewSource</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span>
    <span class="nx">r2</span> <span class="o">:=</span> <span class="nx">rand</span><span class="p">.</span><span class="nx">New</span><span class="p">(</span><span class="nx">s2</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Print</span><span class="p">(</span><span class="nx">r2</span><span class="p">.</span><span class="nx">Intn</span><span class="p">(</span><span class="mi">100</span><span class="p">),</span> <span class="s">&quot;,&quot;</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Print</span><span class="p">(</span><span class="nx">r2</span><span class="p">.</span><span class="nx">Intn</span><span class="p">(</span><span class="mi">100</span><span class="p">))</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">()</span>
    <span class="nx">s3</span> <span class="o">:=</span> <span class="nx">rand</span><span class="p">.</span><span class="nx">NewSource</span><span class="p">(</span><span class="mi">42</span><span class="p">)</span>
    <span class="nx">r3</span> <span class="o">:=</span> <span class="nx">rand</span><span class="p">.</span><span class="nx">New</span><span class="p">(</span><span class="nx">s3</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Print</span><span class="p">(</span><span class="nx">r3</span><span class="p">.</span><span class="nx">Intn</span><span class="p">(</span><span class="mi">100</span><span class="p">),</span> <span class="s">&quot;,&quot;</span><span class="p">)</span>
    <span class="nx">fmt</span><span class="p">.</span><span class="nx">Print</span><span class="p">(</span><span class="nx">r3</span><span class="p">.</span><span class="nx">Intn</span><span class="p">(</span><span class="mi">100</span><span class="p">))</span>
<span class="p">}</span>
</pre></div>

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          <div class="highlight"><pre><span class="gp">$</span> go run random-numbers.go
<span class="go">81,87</span>
<span class="go">0.6645600532184904</span>
<span class="go">7.123187485356329,8.434115364335547</span>
<span class="go">0,28</span>
<span class="go">5,87</span>
<span class="go">5,87</span>
</pre></div>

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            <p>有关 Go 提供的其他随机数的信息，
请参阅 <a href="http://golang.org/pkg/math/rand/"><code>math/rand</code></a> 包文档。</p>

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